The present invention relates generally to disk drives for storing data. More specifically, the present invention relates to a head stack assembly and an E-block that decrease track misregistration.
Disk drives are widely used in computers and data processing systems for storing information in digital form. These disk drives commonly use one or more rotating storage disks to store data in digital form. Each storage disk typically includes a data storage surface on each side of the storage disk. These storage surfaces are divided into a plurality of narrow, annular, regions of different radii, commonly referred to as xe2x80x9ctracksxe2x80x9d. Typically, an E-block having one or more actuator arms is used to position a data transducer proximate each data storage surface of each storage disk. Each data transducer is secured to one actuator arm with a suspension assembly. The data transducer is positioned at a target track on the storage surface in order to access information from, or transfer information to, the storage disk. The E-block is moved with an actuator motor relative to the storage disks. Depending upon the design of the disk drive, each actuator arm can retain one or two transducer assemblies.
The accurate and stable positioning of each data transducer near each data storage surface is critical to the transfer and retrieval of information from the disks. As a result thereof, vibration in the E-block, the suspension assemblies and the storage disks can cause errors in data transfers due to inaccuracies in the positioning of the data transducers relative to the storage disks. This is commonly referred to as xe2x80x9ctrack misregistration.xe2x80x9d The desire to increase performance characteristics of disk drives has resulted in increased rotational velocity of storage disks. Unfortunately, as disk speeds increase, aerodynamic forces also increase. This causes the storage disks to vibrate in the vertical direction, commonly referred to as xe2x80x9cout-of-planexe2x80x9d movements. Such movements can result in an increased difficulty of maintaining the data transducer on the target track and increased inaccuracies in data transfers.
Further, the E-block, suspension assemblies, and the storage disks have modes of vibrations that cause track misregistration. Some of these modes of vibration are prevalent due to the existence of a kinematic relationship between the actuator arms, the suspension assemblies and the storage disks. More specifically, as the storage disk moves vertically because of out-of-plane irregularities of the storage disk, the suspension assembly hinges and the data transducer moves with respect to the surface of the storage disk. This off-track motion is extremely difficult or impossible to follow with the actuator motor.
Moreover, the vibrational forces on the storage disks cause the storage disks to deviate from its usual rotational plane and displacement of the data transducer from the target track. This displacement occurs in both an out-of-plane direction, as well as in a radial direction. The data transducer attempts to follow the disk contour, but in so doing, the data transducer moves off-track, resulting in track misregistration. Therefore, the radial and out-of-plane movements are said to be xe2x80x9ccoupledxe2x80x9d to the track misregistration parameter. Such coupling occurs in disk drives where the storage disks and the actuator arms rotate in parallel planes.
A detailed description of the various problems associated with track misregistration due to vibration of the E-block, suspension assemblies, and out-of-plane motion of the storage disks is provided in U.S. Pat. No. 6,088,192, issued to Riener et al., and assigned to Quantum Corporation, the assignee of the present invention. The contents of U.S. Pat. No. 6,088,192 are incorporated herein by reference.
One attempt to reduce off track motion of the data transducer includes angling the suspension assembly and the data transducer in a roll direction. However, the arm bending mode of the E-block introduces an off-track component that is not significantly impacted by providing a roll angle to the suspension assembly and the data transducer.
Another attempt to minimize off track motion of the data transducer involves using thicker storage disks to minimize disk vibration. However, this design results in a greater thickness of the overall disk drive, and increased costs in manufacturing the disk drive.
Yet another attempt to reduce off track motion of the data transducer includes the addition of microactuators to adjust the position of the data transducers to compensate for the movements of the data transducers relative to the target track. Unfortunately, the addition of microactuators is costly, and further adds another level of complexity to the disk drive. Moreover, microactuators and the necessary electrical circuitry can require additional space within the drive housing, which can make such implementation difficult.
Still another attempt includes the addition of baffles to disrupt airflow across the actuator arms, the suspension assemblies, and disk motion induced by air turbulence. Unfortunately, this design is also not completely satisfactory.
In light of the above, there is the need for a disk drive, head stack assembly, and an E-block that minimizes track misregistration. Additionally, there is a need to provide an E-block having improved vibration and resonance characteristics, and which improves the performance of the disk drive. Further, there is a need for a head stack assembly that closely and accurately follows a data track despite out-of-plane disk motion, vibration of the actuator arms and/or vibration of the suspension assemblies. Moreover, there is a need for a head stack assembly having improved track-following characteristics that are relatively easy and inexpensive to manufacture.
The present invention is directed to an E-block and a head stack assembly for a disk drive. The E-block includes an actuator hub and a first actuator arm secured to the actuator hub. The first actuator arm maintains a first data transducer near a first storage disk. Uniquely, the first actuator arm has a roll-bias angle along the majority of the length of the first actuator arm. The roll-bias angle has an absolute value of greater than zero degrees relative to the first storage disk. Preferably, the roll-bias angle is incorporated into substantially the entire length of the first actuator arm.
Importantly, by incorporating the roll-bias angle into the majority of the length of the first actuator arm, vibration of the first actuator arm and out-of-plane motion of the rotating first storage disk will have a reduced effect on the accurate positioning of the first data transducer relative to the first storage disk.
As used herein, the term xe2x80x9croll-bias anglexe2x80x9d refers to the angle formed by the actuator arm relative to the plane of a storage surface of the storage disk. A negative roll-bias angle is present when a spindle side of the actuator arm is closer to the storage surface of the storage disk than a perimeter side of the actuator arm. In other words, the actuator arm is xe2x80x9ctiltedxe2x80x9d toward a disk axis of the storage disk. A positive roll-bias angle occurs when the actuator arm is tilted in the opposite direction, i.e. away from the disk axis of the storage disk.
As used herein, the term xe2x80x9cskew anglexe2x80x9d refers to the orientation of the actuator arm and the attached data transducer relative to the storage disk. A xe2x80x9czero skew anglexe2x80x9d occurs when a longitudinal axis of the actuator arm forms a ninety degree angle with a radial line from the disk axis to the data transducer. At a zero skew angle, the longitudinal axis of the actuator arm is coplanar with a line that is tangent to a curve of the track immediately adjacent to the data transducer. At a zero skew angle, there is no xe2x80x9cstrainingxe2x80x9d of the data transducer to remain on track. At a xe2x80x9cnegative skew anglexe2x80x9d, the longitudinal axis of the actuator arm forms an obtuse angle with the radial line from the disk axis to the data transducer, i.e. the data transducer has moved from zero skew toward an inner diameter of the storage disk. A xe2x80x9cpositive skew anglexe2x80x9d occurs when the longitudinal axis of the actuator arm forms an acute angle with the radial line from the disk axis to the data transducer, i.e. the data transducer has moved from the zero skew toward an outer diameter of the storage disk.
As provided herein, the E-block can also include a second actuator arm positioned between adjacent first and second storage disks. In this embodiment, each actuator arm has a roll-bias angle. Further, in this design, the E-block preferably is molded and includes a separate actuator arm for each storage surface of each of the storage disks.
The head stack assembly includes a first suspension assembly that secures the first data transducer to the first actuator arm. As provided herein, the E-block is designed so that a mounting surface of the first suspension assembly is maintained at a suspension z height that minimizes track misregistration coupling induced vibration due to the arm bending mode at all skew angles. For an 11 mm long suspension assembly, the first suspension assembly is maintained at between approximately 0.40-0.65 millimeters away from the bottom of the transducer assembly when the first storage disk is rotating. This distance is referred to herein as a xe2x80x9csuspension z-heightxe2x80x9d. Importantly, by reducing the z-height, the influence of out-of-plane motion on the position of the data transducer is decreased. More specifically, the lower z-height of the suspension assembly reduces off track motion due to disk bending, reduces outer diameter to inner diameter sensitivity to skew angle, and minimizes coupling of all the actuator arm bending modes. Stated another way, the lower suspension z-height affects the skew sensitivity to the first arm bending and the disk mode coupling and reduces the track misregistration in one direction of skew to zero. In summary, by maintaining this reduced suspension z-height, the data transducer is more accurately maintained on the target track of the storage disk.
Typically, the head stack assembly includes a base plate that secures the first suspension assembly to the E-block. The base plate includes a beam mount area that engages the second beam surface of the first suspension assembly and a plate mount area that engages the actuator arm. In one embodiment, the beam mount area substantially faces the storage surface of the storage disk and the plate mount area faces in a direction that is substantially opposite the beam mount area and the storage surface of the storage disk. With this design, the base plate is positioned between the E-block and the suspension assembly and the suspension z-height of the suspension assembly is reduced by the thickness of the base plate. As a consequence thereof, the off track movement of the data transducer is reduced.
As provided herein, the arm mode sensitivity plot is approximately zero coupling at a zero skew angle, however, the disk mode coupling is at approximately 3.8% coupling at zero skew angle. Thus, adjusting the suspension Z-height alone will not completely eliminate the track misregistration of the disk modes. Preferably, in order to reduce the disk mode track misregistration, the actuator arms are also rolled.
The present invention is also directed to a method for manufacturing an E-block and a method for manufacturing a head stack assembly for a disk drive.